Display screen or portion thereof with a graphical user interface



The single FIGURE is a front view of a display screen or portion thereof with a graphical user interface, in accordance with the present design.

The broken lines in the single FIGURE showing the display screen or portion thereof and graphical user interface represent portions that form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 